Investigation of the Failure Behavior of Fiber-Reinforced Patches in the Repair of Locally Damaged Steel Pipes

In the present work, we investigate the performance of fiber-reinforced patches in the repair of a locally damaged steel pipe. The specimen of the study was presented for hydrostatic tests before damage and after repair. Damage was generated as a through-thickness cut acting diagonally to the pipe axis. The repair patch comprised twelve layers of fiberglass plain weave fabric aligned orthogonally to the pipe axis. The layers were divided into four distinct sizes and overlapped in a stepped configuration. The inner layers (one to four) covered a surface equivalent to 120% of the damaged area, the subsequent layers (five to seven) covered 160% and then (eight to ten) 200%, and the top layers (eleven and twelve) covered 240%. The hydrostatic tests were conducted until the maximum admissible pressure for the undamaged steel pipe. Two piezoelectric sensors and four strain gages were used in the pipe's instrumentation. The signal obtained during the successive tests was processed in terms of acoustic emission. The repair patch successfully survived the test scenario and acoustic emission detected no significant events. The repair patch robustness was accessed by incrementally degrading its surface and resubmitting the repaired pipe to the hydrostatic test. In the first repair degradation phase, a quarter of the patch's surface (three top layers) was removed through mechanical abrasion. The test was re-conducted, and the patch proved efficient, supporting the maximum admissible pressure once again. The repair patch only failed after degrading half of its surface (middle and top layers). A liquid penetrant test was used to demonstrate the patch's failure, which occurred in the borders of the through-thickness cut. Furthermore, the damage presence was not detected using a borescope.